Performs INS timestep advancement.
The blockList and blockCount arguments tell this routine on
which blocks and on how many to operate. blockList is an
integer array of size blockCount that contains the local
block numbers of blocks on which to advance.
dt gives the timestep through which this update should advance,
and timeEndAdv tells the time that this update will reach when
it finishes. dtOld gives the previously taken timestep.

ARGUMENTS

blockCount - the number of blocks in blockList
blockList - array holding local IDs of blocks on which to advance
timeEndAdv - dummy consistent with toplayer stub function
dt - timestep
dtOld - dummy consistent with toplayer stub function
sweepOrder - dummy argument for the unsplit scheme, just a dummy
variable to be consistent with a top-layer stub function